A vector graphic is a page description object which has been widely used in the prepress field. The vector graphic can be used to revert the original intention of a describer accurately since it has high fidelity during the coordinate transformation. Characters are another page description object which has been widely used in the prepress field, and the internal description data of which are also based on the vector graphic. Therefore, the rasterization of the vector graphic is a core procedure of the whole prepress output system.
The main task of rasterizing a vector graphic is to convert a vector description in a user coordinate space into bitmap information in a device coordinate space. After the conversion into the bitmap information, the generated bitmap information can then be further processed by using a back-end device to improve the quality of the final output bitmap, and during this procedure the boundary information of the graphic is very helpful to the application of the procedure. Therefore, if certain pixels are known to be the boundary pixels of a vector graphic, these pixels can be processed specially so that the output quality of the vector graphics can be improved and a distortion phenomenon of the graphic which may occur on the boundary can be compensated. Based on the similar principle, if certain pixels are known to be the boundary pixels of a character, these pixels can also be processed specially so that the output quality of the character with a low resolution can be improved.
In a black-white binarized bitmap, the boundary means the set of the boundary pixels, whereas a boundary pixel is a black pixel, and at least one of the four pixels adjacent to said black pixels at the upper side, the lower side, the left side and the right side is a white pixel. In accordance with such a definition, the method of performing determination pixel-by-pixel is employed to generate a boundary in the related art, but this method has a deficiency that much more storage space and computation time has to be occupied and the implementation efficiency is very low. Meanwhile, in a practical situation, for the risk is higher when generate the boundary by modifying the core algorithm for rasterizing directly, in the related art, generally, the generation of the boundary is not performed until the vector graphic has been rasterized. However, since the quantity of bitmap data is large at this time, the processing of the bitmap data consumes a great amount of space and time resource, and the efficiency is very low. The effect obtained in the quality improvement, view as a whole, is not enough to counteract the reduction in the processing speed, thus this method is hard to be applied to practical production. At present, with the large increasing in the speed of a back-end output device, a quick and effective method for generating a boundary is imminently required.
However, there is not a technology for generating a boundary which can meet these requirements in the related art.